soft-brightness VS ddcutil

Assuming you're using Gnome, there is for example https://github.com/F-i-f/soft-brightness but note that this will probably just send darker pixels to the screen and not reduce the backlight brightness. Which means your screen will use more power than necessary and picture quality will probably be worse.

Apologies. I hate when people do that as well.

In addition to the other links posted, ddcutil.org has some more good info: https://www.ddcutil.com/#introduction

Sous Linux j'avais utilisé ddcutil

Most monitors have a Virtual Control Panel (VCP), which implements features defined in the Monitor Control Command Set (MCCS). This is a VESA standard. You can find the Input selection command in table 8-10. You send these commands over an I2C bus called Display Data Channel/Command Interface which is yet another VESA standard. If you are running Windows https://www.nirsoft.net/utils/control_my_monitor.html will let you use every VCP feature your monitor has. For Linux, https://www.ddcutil.com/ does this. For Mac, https://github.com/alin23/Lunar

The protocol is called DDC , it's a VESA standard. In there, it's called VCP features. If you are running Windows https://www.nirsoft.net/utils/control_my_monitor.html will let you use every VCP feature your monitor has. For Linux, https://www.ddcutil.com/ does this. For Mac, https://github.com/alin23/Lunar note how all three mention input selection.

ddcutil (a command-line tool, and what most UI tools are based on)

A related non rust tool (that also has an optional GUI) is ddcutil. How does this compare to that?

I've also used ddcui: https://www.ddcutil.com/#introduction, available as an AUR package: https://github.com/rockowitz/ddcutil. This has a nice GUI: https://www.ddcutil.com/screenshots/ddcui_features.png and works on everything I've tried it on out of the box.